The NCA said it built up “intelligence packages” on suspects and sent them to police forces across Britain.

In West Yorkshire, 21 arrests have been made for the possession of indecent images of children.

All of the men have been bailed pending continuing enquiries as part of the operation which has been ongoing in West Yorkshire since April.

Detective Chief Inspector Andy Williams of West Yorkshire Police, said: “West Yorkshire Police have carried out arrests within the West Yorkshire area as part of this national operation and our enquiries at a local level very much remain ongoing.

“This has been a significant national operation in which all forces involved have collaborated closely and used a wide variety of investigative techniques.

“Tackling sexual offences and in particular sex offending involving children is an area which West Yorkshie Police has prioritised in recent years and allocated extra resources to. We are committed to investigating all allegations of offences of this type.”

NCA deputy director general Phil Gormley said the crackdown, the biggest ever operation of its kind, involved alleged paedophiles who used the so-called “dark web” as well as traditional internet access.

The “dark web” is internet content that is not listed by normal search engines. Users will often use payment methods such as virtual currencies to help avoid detection.

The 431 children who were safeguarded were in the “care, custody or control” of the suspects, and included 127 who were deemed to be at immediate risk of harm.

Mr Gormley said he was “profoundly disappointed” that so many suspects had been arrested over this type of crime, and said a harder look needs to be taken at the high numbers of people accessing child abuse images.

He said: “The alternative is not to look under the stone, and we cannot afford not to look under this stone.”

Claire Lilley, head of online safety at the NSPCC, said: “This is an important two-pronged operation which has rescued children from abuse and also identified many previously unknown sex offenders. Direct action like this sends a strong message to those who subject children to harrowing sexual assaults that they can and will be traced and prosecuted.

“But law enforcement agencies alone cannot deal with the vast problem of illegal images which continue to flood the market. Industry has to find inventive ways of blocking the flow of such horrendous pictures which are only produced through the suffering of defenceless children - many of who are not even old enough to go to school.

“So while this operation must be rightly applauded we should view it as yet another warning sign that far more needs to be done if we are to stem the sordid trade in these images, which are often used by those who go on to abuse children.”